Improve Rust code clarity across the workspace

Document public APIs and non-obvious control flow so the protocol, simulator, and macro crates are easier to follow. Tighten a few helper paths and feature gates while preserving behavior and keeping the workspace warning-free.

ush-obfuscate/src/env.rs

@@ -1,6 +1,9 @@
 const ENV_KEY_NAME: &str = "OBFUSCATION_KEY";
 const BACKUP_ENV_KEY: &str = "OBFUSCATION_KEY_DO_NOT_USE";
 
+/// Returns the obfuscation key used by the proc macros.
+///
+/// The fallback keeps macro expansion deterministic when the environment variable is absent.
 pub fn get_encryption_key() -> String {
     if let Ok(key) = std::env::var(ENV_KEY_NAME) {
         key